The invention relates generally to non-invasive imaging such as single photon emission computed tomography (SPECT) imaging. More particularly, the invention relates to adjustable collimators for use in non-invasive imaging.
SPECT is used for a wide variety of imaging applications, such as medical imaging. In general, SPECT systems are imaging systems that are configured to generate an image based upon the impact of photons (generated by a nuclear decay event) against a gamma-ray detector. In medical and research contexts, these detected photons may be processed to formulate an image of organs or tissues beneath the skin.
To produce an image, one or more detector assemblies may be rotated around a subject. Detector assemblies are typically comprised of various structures working together to receive and process the incoming photons. For instance, the detector assembly may utilize a scintillator assembly (e.g., large sodium iodide scintillator plates) to convert the photons into visible light for detection by an optical sensor. This scintillator assembly may be coupled by a light guide to multiple photomultiplier tubes (PMTs) or other light sensors that convert the light from the scintillator assembly into an electric signal. In addition to the scintillator assembly-PMT combination, pixilated solid-state direct conversion detectors (e.g., CZT) may also be used to generate electric signals from the impact of the photons. This electric signal can be transferred, converted, and processed by electronic modules in a data acquisition module to facilitate viewing and manipulation by clinicians.
Typically, SPECT systems further include a collimator assembly that may be attached to the front of the gamma-ray detector. In general, the collimator assembly is designed to absorb photons such that only photons traveling in certain directions impact the detector assembly. The collimator assembly selected for use with the SPECT system impacts the system performance thereof, including image resolution and sensitivity. Because resolution and sensitivity may be traded off along a collimator performance curve for each SPECT system, a single operating point typically may be selected when designing a collimator assembly. In other words, a collimator assembly is typically designed to operate at a single operating point on the resolution-sensitivity tradeoff performance curve. Different applications, however, may benefit from operating with different tradeoffs on the performance curve. By way of example, small organ imaging typically may require higher resolution and lower sensitivity, whereas imaging a large volume (such as for possible lesions) typically may require higher sensitivity with lower resolution.
To provide a SPECT system with different tradeoffs on the performance curve, multiple collimator assemblies may be provided for each SPECT system with each of the collimator assemblies having a different performance point. In this manner, a user may have a choice in selecting a collimator assembly with an appropriate operating point for a particular application. Accordingly, when the user changes applications, the most appropriate collimator assembly must be mounted on the SPECT system. Collimator assemblies, however, are typically heavy, generally comprising lead with a thickness sufficient to block gamma rays so that the collimator exchange is a time consuming process. To minimize this time-consuming exchange, extra effort may be made to schedule blocks of patients with similar examination requirements, for example, in clinical laboratories. In addition to the problems associate with the time-consuming exchange of the collimator assemblies, the purchase and storage of multiple collimator assemblies is costly.
Accordingly, it would be desirable to provide an imaging system with collimator assemblies having different operating points along the resolution-sensitivity tradeoff performance curve while reducing the need for multiple collimator assemblies.